In light of energy demand and environmental concerns, processes and compositions for the production of fuels from renewable feedstocks are needed. A common process involves producing ethanol from corn. Unfortunately, using corn and the like as precursors competes with food and feed supplies. Accordingly, other routes are being explored.
One such other route involves acid/hydrolysis of, for example, lignocellulosic biomass followed by, for example, fermentation to produce bioalcohols such as ethanol. Lignocellosic biomass refers to plant biomass that is composed of cellulose, hemicelluloses, and lignin. The carbohydrate polymers (cellulose and hemicelluloses) are tightly bound to the lignin. Lignocellulosic biomass can be grouped into four main categories: (1) agricultural residue (including corn stover and sugarcane bagasse), (2) dedicated energy crops, (3) wood residues (including sawmill and paper mill discards), and (4) municipal paperwaste. Unfortunately, many of these prior art approaches involve the use of or the producing a by-product of, for example, substances which may inhibit or poison heterogeneous catalysts such as noble metal catalysts that are sometimes used in downstream processing. Such substances include, for example, sulfuric acid, organic sulfur compounds, and/or halide ions. In some cases, the prior art approaches use, for example, mineral acids for acid hydrolysis of biomass. Unfortunately, these too may result in residual inorganic salt species and the like which can possibly affect the performance of downstream heterogeneous or enzyme catalysts. What's more, mineral acids may also be corrosive to conventional process equipment, may require the use of expensive alloys, and are generally not considered to be environmentally-friendly or green reagents. Unfortunately, other recent approaches such as those described in, for example, WO 2009/060126; WO 2009/080737; and 2009/092749 have one or more other disadvantages such as requiring concentrated acids or mixtures of acids, low yields, degradation of desirable products such as soluble monosaccharides, and/or complex processing conditions.
Accordingly, it would be desirable to discover new processes and compositions that could be employed in, for example, the production of fuels from renewable feedstocks. It would be advantageous if such processes and compositions did not require substances which may inhibit or otherwise affect the performance of downstream heterogeneous or enzyme catalysts. It would further be advantageous if the substances employed were less corrosive, more environmentally-friendly, effective at lower concentrations, and/or produced high yields without degrading desirable products and without the use of complex processing conditions.
Fortunately, the present inventors have discovered new processes and compositions which may meet one or more of the aforementioned needs or even have other advantages. In one embodiment, the invention relates to a process for treating a feedstock comprising holocellulose. The process comprises mixing the feedstock with an aqueous acid solution to form a mixture which has an initial pH at 25° C., i.e., pH25° C., of from about 1 to about 3. The acid comprises from about 1 to about 30 percent by weight based on the total weight of the aqueous acid solution. The acid is comprised of at least about 90% by weight of formic acid based on the total weight of the acid. Next, the mixture is subjected to conditions sufficient to produce a hydrolysis product comprising monosaccharides and water-soluble oligosaccharides. The sum of monosaccharides and water-soluble oligosaccharides is at least about 50% by weight of the total holocellulose in the feedstock.
In another embodiment, the invention relates to a composition suitable for bioalcohol production. The composition comprises a feedstock comprising holocellulose and an aqueous acid solution comprising at least about 90% formic acid based on total acid weight. The composition has a pH25° C.of from about 1 to about 3. The acid comprises from about 1 to about 30 percent by weight based on the total weight of the aqueous acid solution.